The present invention generally relates to an odometer apparatus, and more particularly to an odometer apparatus in which a figure representing travel distance traveled by a motor vehicle is indicated, the figure with a set of digits each being indicated by the amount of rotation of each of several indication gears cooperatively coupled with several pinions.
A prior art odometer apparatus as shown in FIGS. 1 and 2 includes a frame 1, two parallel supporting shafts 2, 3 provided within the frame 1, a plurality of indication gears 41 to 46, a plurality of pinions 5, a worm gear shaft 8, a transmitting gear 9, and a drive gear 10. The worm gear shaft 8 is rotated by a drive motor in accordance with the travel distance traveled by a vehicle, and a rotating force from the worm gear shaft 8 is transmitted to the plurality of pinions 5 via the drive gear 10 and the transmitting gear 9. The indication gears 41 to 46 are rotated around the supporting shaft 2 respectively by the pinions 5 in accordance with the travel distance traveled by the vehicle. Each of several digits in an indication figure representing the travel distance of the vehicle is described by the amount of rotation of each of the indication gears 41 to 46.
As shown in FIGS. 1 and 2, the transmitting gear 9 has two shift teeth 7 formed on one side thereof and each of the indication gears 41 to 46 has a number of connecting teeth 6 formed on one side thereof and two shift teeth 7 formed on the opposite side thereof. And, a plurality of pinions 5 are rotatably supported on the supporting shaft 3, and the teeth 6 and the two shift teeth 7 are engaged with the indication gears 41 to 46 so that the teeth 5b of the pinions 5 are engaged with the two shift teeth 7 of the indication gears 41 to 46 and with the connecting teeth 6 of an indication gear next to one of the other indication gears, so the rotating movement of the pinions 5 is coordinated with that of the indication gears 41 to 46. A number of boss portions 5a are formed along the supporting shaft 3, each of the boss portions 5a being arranged between two adjacent pinions 5 and having a cross section of a generally square shape as shown in FIG. 2.
Also provided in the odometer apparatus are a number of pressure members 11 aligned along the supporting shaft 3. These pressure members 11, which may be, for example, leaf springs, are fixed to the frame 1 at one end thereof and opposed to the boss portions 5a having a generally square cross section at the other end thereof. Since the pressure members 11 operate to keep the pinions 5 at the same rotation phase around the supporting shaft 3 by applying pressure to the boss portions 5a, the prior odometer apparatus can prevent the occurrence of an error in the indication figure due to the backlash between the gears 41 to 46 and the pinions 5. In the case of the prior odometer apparatus, each of the pressure members 11 is parallel to and snugly in contact with a side surface of the boss portion 5a to exert appropriate pressure for eliminating an error in the figure due to the backlash between the gears and the pinions.
However, the pressure members 11 of the prior odometer apparatus are arranged to press completely a side surface of each of the boss portions 5a supported on the supporting shaft 3 to eliminate the indication figure error due to the above described backlash, and the pressure members 11 show a relatively great deflection, thereby requiring a large load torque to operate the odometer apparatus. FIG. 3 is a characteristic chart showing the load torque of the prior art odometer apparatus shown in FIGS. 1 and 2 with respect to the pinion rotation angle. As shown in FIG. 3, the peak load torque or the maximum load torque appears when the pinion is rotated about 10 degrees from the initial position (when the pinion rotation angle is equal to 0 deg), the level of the maximum load torque being approximately twice that of the initial load torque when the pinion is at the initial position. This means that the conventional odometer apparatus requires a drive torque which is twice as large as that of the load torque required for preventing an error in the indication figure from occurring due to the above described backlash. Thus, the prior odometer apparatus has a problem in that a relatively large drive torque must be applied to the odometer apparatus, and it is difficult to construct a compact apparatus because a drive motor being used has to be relatively large in size. In the case of a motor drive type odometer apparatus, because a drive motor for applying drive torque to the odometer apparatus must output a relatively large torque, the odometer apparatus including the drive motor has to be large in size, and the manufacturing cost thereof is thus increased.
In addition, the prior art odometer apparatus usually has a reverse rotation prevention mechanism, which is disclosed, for example, in Japanese Published Patent Application No. 54-10468. In this reverse rotation prevention mechanism, a plurality of indication gears are rotatably supported on a first shaft, and a plurality of pinions are rotatably supported on a second shaft, each of the indication gears being formed into an asymmetrical shape, a number of connecting teeth being formed on one side of each indication gear and two shift teeth formed on the opposite side thereof. Adjacent to the two shift teeth of the indication gears, there are respectively provided a set of stepped surfaces for preventing the reverse rotation of the indication gears. In a normal operation, the indication gears are rotated around the first shaft in the forward direction to indicate an indication figure. When the indication gears are rotated in the reverse direction, the teeth of the pinions 5 strike the stepped surfaces of the indication gears and are connected with the teeth of the pinions 5, thus preventing the indication gears from being rotated in the reverse direction.
However, the prior art odometer apparatus described above has a problem in that the indication gears having the two shift teeth and the stepped surfaces have a complicated shape and the cost of the odometer parts is thus increased. In addition, when the odometer having the reverse rotation prevention mechanism is inspected in an inspection line for checking the quality of finished products, it is difficult to reversely rotate the indication gears, which makes the inspection of the finished products inconvenient.